Transcription of Capacitive Touch Using Only an ADC (CVD) App. Note
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Capacitive Touch Using Only an ADC (CVD) App. Note
AN1298. Capacitive Touch Using only an ADC ( CVD ). Sensing Steps Authors: Thomas Perme Dieter Peter To perform the sensing, do the following: Microchip Technology Inc. 1. Drive secondary channel to VDD as digital output. INTRODUCTION 2. Point ADC to the secondary VDD pin (charges CHOLD to VDD). This application note describes a new hardware 3. Ground sensor line. sensing method called Capacitive Voltage Divider 4. Turn sensor line as input (TRISx = 1). (CVD) which uses no external components. It requires 5. Point ADC to sensor channel (voltage divider only the ADC to perform Capacitive Touch sensing. The from sensor to CHOLD). principle is simple, and can be applied to nearly any Microchip PIC device with an ADC. 6. Begin ADC conversion. 7. Reading is in ADRESH:ADRESL. THEORY OF OPERATION Sensing Steps Description Sensor construction is the same as a typical sensor; a The basic principle begins with one ADC channel sensor is an area of copper on a PCB or similar charging the internal sample-and-hold cap for the ADC.
AN1298 DS01298A-page 2 © 2009 Microchip Technology Inc. FIGURE 2: CVD BLOCK DIAGRAM (STEP 5) Detecting a Touch A touch will cause the ADC reading to decrease.
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